U.S. patent application number 15/022829 was filed with the patent office on 2016-08-11 for crossover valve system and method for gas production.
This patent application is currently assigned to RAISE PRODUCTION INC.. The applicant listed for this patent is RAISE PRODUCTION INC.. Invention is credited to Eric LAING, Geoff STEELE.
Application Number | 20160230520 15/022829 |
Document ID | / |
Family ID | 52812408 |
Filed Date | 2016-08-11 |
United States Patent
Application |
20160230520 |
Kind Code |
A1 |
STEELE; Geoff ; et
al. |
August 11, 2016 |
CROSSOVER VALVE SYSTEM AND METHOD FOR GAS PRODUCTION
Abstract
A crossover valve assembly for insertion into production tubing,
or integral with production tubing, includes an outer housing, an
inner production tube, a pilot section responsive to external
pressure to open an activation passage above a pre-determined
pressure, a power section responsive to pressure in the activation
passage to open an injection opening; and a crossover valve
responsive to pressure in the injection opening to open a crossover
port, allowing fluid communication from outside the outer housing
to within the inner production tube. The crossover valve assembly
may be used in a method of producing a vertical, deviated or
horizontal gas well having an annular space defined by a well
casing and a concentrically disposed production tubing, wherein an
annulus exists above a packer isolating the annulus, includes the
steps of (a) opening a communication path through the tubing into
the annulus, and if necessary, removing any fluid in the annulus,
(b) landing a crossover valve assembly within the production tubing
above the packer and exposed to the annulus; and (c) injecting gas
into the annular space to open the crossover valve and enter the
production tubing, wherein the injected gas lifts liquids in the
production tubing to the surface.
Inventors: |
STEELE; Geoff; (Calgary,
CA) ; LAING; Eric; (Calgary, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RAISE PRODUCTION INC. |
|
|
|
|
|
Assignee: |
RAISE PRODUCTION INC.
Calgary
AB
|
Family ID: |
52812408 |
Appl. No.: |
15/022829 |
Filed: |
October 14, 2014 |
PCT Filed: |
October 14, 2014 |
PCT NO: |
PCT/CA2014/050990 |
371 Date: |
March 17, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61889768 |
Oct 11, 2013 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 43/121 20130101;
E21B 34/10 20130101; E21B 34/102 20130101; E21B 43/123 20130101;
E21B 33/12 20130101; F16K 31/426 20130101 |
International
Class: |
E21B 43/12 20060101
E21B043/12; E21B 33/12 20060101 E21B033/12; E21B 34/10 20060101
E21B034/10 |
Claims
1. A method of producing a vertical, deviated or horizontal gas
well having an annular space defined by a well casing and a
concentrically disposed production tubing, said well having an
annulus and a lower producing zone open to the production tubing,
wherein the annulus is isolated from the lower producing zone by a
packer, comprising the steps of: (a) opening a communication path
through the tubing into the annulus, and if necessary, removing any
fluid in the annulus; (b) landing at least one crossover valve
within the production tubing exposed to the annulus, wherein the
crossover valve has a pilot section having a predetermined closing
pressure, a power section and a crossover fluid passage; and (c)
injecting gas into the annulus to at least the closing pressure to
activate the pilot section, thereby exposing the power section to
the annulus, thereby opening the crossover fluid passage and
allowing injected gas to enter the production tubing, wherein the
injected gas lifts liquids in the production tubing to the
surface.
2. The method of claim 1 wherein the at least one crossover valve
is deployed on a continuous or jointed tubing string or by
wireline, within the production tubing.
3. The method of claim 1 wherein the gas is injected continuously
or the gas is injected periodically.
4. The method of claim 3 wherein the gas is injected in response to
pre-determined conditions in the wellbore, including the position
of a plunger, pressure in the annulus, pressure or gas flow in the
production tubing, tubing fluid levels or pressure differential
between the tubing and annulus.
5. The method of claim 1 wherein the injected gas comprises
instrumentation sweet gas.
6. A crossover valve assembly for insertion into production tubing,
or integral with production tubing, comprising: (a) an outer
housing; (b) an inner production tube; (c) a pilot section
responsive to external pressure above a pre-determined pressure, or
responsive to an electrical actuator, to open an activation
passage; (d) a power section responsive to pressure in the
activation passage to open an injection opening; and (e) a
crossover valve responsive to the external pressure to open a
crossover port, allowing fluid communication from outside the outer
housing to within the inner production tube.
7. The crossover valve assembly of claim 6 wherein the
pre-determined pressure is set by means of a mechanical spring, or
a gas spring, or both a mechanical and gas spring, acting within
the pilot section.
8. The crossover valve assembly of claim 7, wherein the
pre-determined pressure is set at least partially by a gas spring,
and wherein the gas spring is connected to a pilot gas supply by a
pilot gas regulator, which is configured to charge or discharge the
gas spring to vary the pre-determined pressure.
9. The crossover valve assembly of claim 6 wherein the power
section comprises an equalization pathway open to outside the outer
housing, which equalization pathway is more restrictive to gas flow
than the activation passage.
10. The crossover valve assembly of claim 6, comprising: (a) a
pilot section comprising an outer housing and an inner production
tube disposed concentrically within the outer housing, defining an
annular space therebetween, a pilot valve assembly within the
annular space and comprising a valve seat and a pilot piston
moveable between a closed position and an open position, a pilot
chamber exposed through a pilot opening in the outer housing, and a
spring for biasing the pilot piston towards the closed position;
(b) a power section comprising an outer housing and an inner
production tube disposed concentrically within the outer housing,
defining an annular space therebetween, a power valve assembly
disposed within the annular space and comprising a valve seat, a
valve mandrel and an activation piston, wherein the valve mandrel
and an activation piston are moveable between a closed position and
an open position, wherein the power section defines an activation
chamber; (c) an activation fluid passage between the pilot chamber
and the activation chamber which is closed when the pilot piston is
in its closed position and open when the pilot piston is in its
open position, and wherein fluid pressure in the activation fluid
passage moves the activation piston and valve mandrel to their open
position; (d) a crossover fluid passage through the power section
outer housing and the power section inner production tube, which is
closed when the activation piston and the valve mandrel are in
their closed position and open when the activation piston and the
valve mandrel are in their open position; and (e) an equalization
fluid passage between the activation chamber and through the power
section outer housing, which equalization passage is more
restrictive than the activation fluid passage.
11. The crossover valve assembly of claim 10 wherein the spring for
biasing the pilot piston comprises a mechanical spring or a gas
spring, or both a mechanical spring and a gas spring.
12. The crossover valve assembly of claim 8 further comprising an
electrical control module operatively connected to a remote
controller, comprising a solenoid and pilot pressure regulator,
which opens to expose the pilot section to external pressure, and
closes to isolate the pilot section from external pressure.
13. The crossover valve assembly of claim 11 further comprising an
electrical control module operatively connected to a remote
controller, comprising a pilot gas supply line and a pilot gas
regulator, for remotely charging or discharging the gas spring.
14. A crossover valve assembly for insertion into production
tubing, or integral with production tubing, comprising: (a) an
outer housing; (b) an inner production tube; (c) a pilot section
responsive to an electrical actuator to open an activation passage,
which is then open to external pressure; (d) a power section
responsive to pressure in the activation passage to open an
injection opening; and (e) a crossover valve responsive to external
pressure to open a crossover port, allowing fluid communication
from outside the outer housing to within the inner production tube
.
15. The crossover valve assembly of claim 14 wherein the electrical
actuator is responsive to a signal from a remote controller or a
signal from a pressure transducer, or both.
16. A system for producing a vertical, deviated or horizontal gas
well having an annular space defined by a well casing and a
concentrically disposed production tubing, said well having an
annulus and a lower producing zone open to the production tubing,
wherein the annulus is isolated from the lower producing zone by a
packer, comprising: (a) a communication path through the tubing
into the annulus; (b) at least one crossover valve within the
production tubing exposed to the annulus through the communication
path; (c) a surface gas injector and a gas supply for injecting gas
into the annular space to open the crossover valve and enter the
production tubing; (d) a plunger for reciprocating within the
production tubing; and (e) a surface controller for controlling the
gas injector, wherein the controller is responsive to a signal
indicative of one or more of the following: the position of the
plunger, pressure in the annulus, pressure or gas flow in the
production tubing, tubing fluid level or pressure differential
between the tubing and annulus.
17. The system of claim 16 wherein the gas supply comprises sweet
instrumentation gas.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to a valve and a method to
enhance production from gas wells, and particularly gas wells with
low flow pressures and inconsistent production line pressure.
BACKGROUND
[0002] Gas wells, and in particular sour gas wells with varying
quantities of H.sub.2S are produced throughout the Western Canada
Sedimentary Basin. Even when reservoir pressures deplete, the
remaining gas volumes left in the reservoir are usually
significant. The challenge is to produce the remaining reserves
with low flowing pressures and inconsistent production line
pressures.
[0003] Sour gas wells are typically completed with a packer in
place to isolate the sour production from the annular space between
the well casing inside diameter and the outside diameter of the
production tubing. The packer prevents sour gas from entering the
annulus and corroding the casing string, which is the barrier
between the wellbore and any adjacent ground water or aquifer.
Additionally, the annulus above the packer is typically filled with
inhibited brine solution to enhance corrosion protection and
provide an additional barrier preventing migration of sour gas into
the annulus.
[0004] All gas wells will produce a quantity of liquid during gas
production. Liquid loading is a symptom of the well's inability to
unload liquids that are naturally produced during the production
life of the well and is the most common cause of production decline
in a gas well. In addition to liquid loading, there are a number of
other reasons why wells will not produce at the maximum level. If a
number of wells are drilled into the same reservoir and the gas is
depleted at a faster than normal rate, the competitive drainage of
the reservoir will reduce production. In a compartmentalized
reservoir, where reservoir size is limited because of lack of
connectivity between the permeable parts of the formation, there
may be production issues. Also, production may be limited because
of formation damage caused to the near well bore while drilling the
well or on subsequent work over with a service rig or natural near
well bore damage may also be caused by liquid loading or natural
scaling effects of the produced well effluent.
[0005] When a well is initially drilled, it is typically in a
virgin part of the reservoir, and therefore reservoir pressures and
volumes are usually quite high. The surface production lines that
will transport the gas and liquids are operated at pressures that
allow the well to flow to surface. The difference between the
surface lines pressure and the flowing bottom hole pressure of the
well will dictate how much the well can flow. Other factors also
relate directly to this such as gas density, friction effect,
liquid density and depth of the well. As the well ages and flowing
bottom hole pressure depletes, the well will experience reduced
flow capability.
[0006] It is well known that liquid loading affects gas production
when gas velocity drops below the level necessary to carry liquid
droplets upwards, known as the critical gas velocity. Critical gas
velocity is a function of flowing pressure, fluid and gas density,
droplet size, surface tension, temperature and pipe diameter.
[0007] One method of increasing gas velocity is to change tubular
size or decrease surface pressure, and the effect on the wells
ability to unload liquid can be dramatic when such solutions are
applied. However, these solutions will only last as long as the
bottom reservoir pressure can produce against the new
conditions.
[0008] Unfortunately for most sour gas wells, the option to change
tubulars or decrease surface pressures is often uneconomic, and the
well is abandoned long before its usable reserves are depleted. The
cost to change out tubulars is high (rig, safety equipment, pump
trucks etc.) and there is a significant risk of potential damage to
the formation, which may occur as the well has to be killed using a
fluid having hydrostatic weight equal or greater than the shut in
reservoir pressure. In many cases the depth of the well and the low
reservoir pressure will not hold a full column of kill fluid and
the fluid will fracture into the formation face, causing damage
that cannot be repaired.
[0009] Surface pressure may be reduced by using a compressor to
reduce the flowing wellhead pressure in the wellbore. The cost is
directly related to the size of compressor required to have
sufficient suction pressure that allows the well to unload liquid
with the elevated velocity required to produce the gas to the
gathering system lines. Most compressors for sour gas are required
to have numerous safety shutdown systems and expensive coolers to
reduce the heat of compressed gas and noise emission controls.
[0010] Artificial lift in these wells is difficult to implement.
Most types of downhole mechanical or electrical pumps do not work
well in a high gas environment due to gas locking and cavitation.
The costs of the modifications or additional completion components
required to adapt the pumping systems to efficient operation in
high gas ratio environments can also be prohibitively
expensive.
[0011] Therefore, there is a need in the art for an innovative and
economical solution to produce gas from these aging reservoirs.
SUMMARY OF THE INVENTION
[0012] In one aspect, the invention comprises a down hole crossover
valve as part of an operational system that uses reservoir energy
and injected gas to produce gas. In one embodiment, the produced
gas and injected gas may activate a plunger which reciprocates up
and down the well bore, which acts as interface between the
produced liquid and produced gas, thereby unloading all liquid to
surface. The plunger may be cycled numerous times throughout the
day and the frequency of cycling is only dependent on how much gas
is available for each cycle.
[0013] Therefore, in one aspect, the invention comprises a method
of producing a vertical, deviated or horizontal gas well having an
annular space defined by a well casing and a concentrically
disposed production tubing, said well having a lower producing zone
open to the production tubing, wherein the annulus is isolated from
the lower producing zone by a packer, comprising the steps of:
[0014] (a) opening a communication path through the tubing into the
annulus, and if necessary, removing any liquid in the annulus;
[0015] (b) landing at least one crossover valve within the
production tubing exposed to the annulus, wherein the crossover
valve has a pilot section having a predetermined closing pressure,
a power section and a crossover fluid passage; and
[0016] (c) injecting gas into the annulus to at least the closing
pressure to activate the pilot section, thereby exposing the power
section to the annulus, thereby opening the crossover fluid passage
and allowing injected gas to enter the production tubing, wherein
the injected gas lifts liquids in the production tubing to the
surface.
[0017] In one embodiment, the at least one crossover valve is
deployed on a continuous or jointed tubing string or by wireline,
within the production tubing.
[0018] In another aspect, the invention may comprise a crossover
valve assembly for insertion into production tubing, or integral
with production tubing, comprising:
[0019] (a) an outer housing;
[0020] (b) an inner production tube;
[0021] (c) a pilot section responsive to external pressure above a
pre-determined pressure to open an activation passage;
[0022] (d) a power section responsive to pressure in the activation
passage to open an injection opening; and
[0023] (e) a crossover valve responsive to the external pressure to
open a crossover port, allowing fluid communication from outside
the outer housing to within the inner production tube.
[0024] In one embodiment, the invention comprises a crossover valve
assembly comprising:
[0025] (a) a pilot section comprising an outer housing and an inner
production tube disposed concentrically within the housing,
defining an annular space therebetween, a pilot valve assembly
within the annular space and comprising a valve seat and a pilot
piston moveable between a closed position and an open position, a
pilot chamber exposed through a pilot opening in the outer housing,
and a spring for biasing the pilot piston towards the closed
position;
[0026] (b) a power section comprising an outer housing and an inner
production tube disposed concentrically within the housing,
defining an annular space therebetween, a power valve assembly
disposed within the annular space and comprising a valve seat, a
valve mandrel and an activation piston, wherein the valve mandrel
and the activation piston are moveable between a closed position
and an open position, wherein the power section defines an
activation chamber;
[0027] (c) an activation fluid passage between the pilot chamber
and the activation chamber, which is closed when the pilot piston
is in its closed position, and open when the pilot piston is in its
open position, and wherein fluid pressure in the activation fluid
passage moves the activation piston and valve mandrel to their open
position;
[0028] (d) a crossover fluid passage through the power section
outer housing and the power section inner production tube which is
closed when the activation piston and the valve mandrel are in
their closed position.
[0029] In one embodiment, the pilot piston is biased in the closed
position by a pre-determined closing pressure created by means of a
mechanical spring such as a coil spring, or a gas spring, or both a
mechanical and gas spring, acting within the pilot section. The
power section may comprise an equalization pathway between the
activation chamber and open to outside the outer housing, which
equalization pathway is more restrictive to gas flow than the
activation passage. In one embodiment, the gas spring is connected
to a gas supply line which can be activated to increase or reduce
the pressure of the gas spring, thereby increasing or reducing the
closing pressure.
[0030] In one embodiment, the crossover valve assembly comprises an
electrical control module operatively connected to a remote
controller, comprising a solenoid and pilot pressure regulator,
which opens to expose the pilot section to external pressure, and
closes to isolate the pilot section from external pressure.
[0031] In one embodiment, the crossover valve assembly further
comprises an electrical control module operatively connected to a
remote controller, comprising a pilot gas supply line and a pilot
gas regulator, for remotely charging or discharging the gas
spring.
[0032] In another aspect, the invention may comprise a system for
producing a vertical, deviated or horizontal gas well having an
annular space defined by a well casing and a concentrically
disposed production tubing, said well having an annulus and a lower
producing zone open to the production tubing, wherein the annulus
is isolated from the lower producing zone by a packer,
comprising:
[0033] (a) a communication path through the production tubing into
the annulus;
[0034] (b) at least one crossover valve within the production
tubing exposed to the annulus through the communication path;
[0035] (c) a surface gas injector and a gas supply for injecting
gas into the annular space to open the crossover valve and enter
the production tubing;
[0036] (d) a plunger for reciprocating within the production
tubing; and
[0037] (e) a controller for controlling the gas injector, wherein
the controller is responsive to a signal indicative of one or more
of the following: the position of the plunger, pressure in the
annulus, pressure, gas flow in the production tubing, tubing fluid
level, or pressure differential between the tubing and the
annulus
[0038] In one embodiment, the at least one crossover valve is
deployed on a continuous or jointed tubing string, within the well
casing. In one embodiment, the system may further comprise a
plunger for reciprocating within the production tubing. The system
may further comprise a controller for controlling the gas injector,
wherein the controller is responsive to a signal indicative of one
or more of the following: the position of the plunger, pressure in
the annulus, pressure or gas flow in the production tubing, tubing
fluid level, or pressure differential between the tubing and the
annulus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] In the drawings, like elements are assigned like reference
numerals. The drawings are not necessarily to scale, with the
emphasis instead placed upon the principles of the present
invention. Additionally, each of the embodiments depicted are but
one of a number of possible arrangements utilizing the fundamental
concepts of the present invention. The drawings are briefly
described as follows:
[0040] FIG. 1 is a schematic representation of a wellbore with an
annulus and lower producing zone, sectioned vertically along its
length and depicting the crossover valve through-tubing
completion.
[0041] FIG. 2 is a schematic representation of the crossover valve
device sectioned along its length to reveal all of the working
components.
[0042] FIG. 3 is a detailed view of area A shown in FIG. 2, showing
the power section valve assembly.
[0043] FIG. 4 is a detailed view of area B of FIG. 2, showing the
pilot section valve assembly.
[0044] FIG. 5 is a tranverse cross-sectional view along line C-C in
FIG. 2.
[0045] FIG. 6 is a cross sectional view of the crossover valve of
FIG. 2, shown with the pilot valve assembly in its open
position.
[0046] FIG. 7 is a cross sectional of the power section of the
crossover valve of FIG. 2, shown with the power valve assembly in
its open position.
[0047] FIG. 8 is a cross sectional of the power section of the
crossover valve of FIG. 2, shown with the RCV valve in its open
position.
[0048] FIG. 9 is a schematic representation of one embodiment of a
crossover valve assembly having an electrical control module.
[0049] FIG. 10 is a schematic representation of one embodiment of a
crossover valve with direct solenoid actuation of the pilot
section.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0050] When describing the present invention, all terms not defined
herein have their common art-recognized meanings. To the extent
that the following description is of a specific embodiment or a
particular use of the invention, it is intended to be illustrative
only, and not limiting of the claimed invention.
[0051] This invention relates to a controllable crossover valve and
systems which incorporate the valve to enhance gas production by
means of gas lift or gas re-circulation workflows. During gas
lift/gas re-circulation workflows, the working fluid comprises
injected gas which moves from outside the production tubing to
within the production tubing.
[0052] In one embodiment, the apparatus of the present invention is
designed to facilitate production of gas wells with low flow
pressures and/or inconsistent production line pressure, and sour
gas wells in particular. However, the term "fluid" is used herein
as comprising both liquids and gases.
[0053] As shown in FIG. 1, a producing gas well comprises a casing
string (1) and a concentric production tubing string (2), defining
an annular space between them. A packer (3) within the annulus
provides a seal between the tubing outside diameter and the casing
inside diameter, and isolates the upper annulus from the producing
zone. The packer prevents cross-flow of produced liquids and gas
above the packer and protects the casing from corrosion usually
associated with H.sub.2S, as the casing is the only barrier between
the wellbore and the surrounding natural formation.
[0054] Many sour gas well sites are equipped with high pressure,
sweet fuel gas for instrumentation operation. This source gas may
also be an excellent medium for annular circulation gas. Therefore,
in one aspect, the invention comprises a method of producing
natural gas from an isolated zone, such as a sour gas zone, by
using injected sweet gas to lift liquids in the production tubing
to the surface. In general terms, in another aspect, the apparatus
of the present invention comprises a crossover valve device, which
opens in response to pressure in the casing annulus, or as result
of direct control, to permit fluid flow from the annulus into the
tubing string.
[0055] The crossover valve assembly (10) comprises a number of
inner tubular elements (11) assembled together to define an
internal production flow path, and an outer housing (12). Various
functional components described below are disposed in the annular
space between the inner tubulars (11) and the outer housing (12).
In one embodiment, the valve assembly comprises a pilot section
(13) and a power section (14), connected by an intermediate pup
joint (16) defining an annular fluid passage (17). In one
embodiment, the valve assembly (10) is adapted to be run on
wireline, or deployed on continuous or jointed tubing string. In
one embodiment, the valve may be an integral component of a tubing
string.
[0056] The pilot section comprises a concentric sliding pilot
piston (18), a pilot valve seat (20) and an annulus pressure
opening (22) in the outer housing (12). In its closed position, as
shown in FIGS. 2 and 4, the downhole end of the pilot piston (18)
is seated against valve seat (20), closing off the pup joint fluid
passage (17) from external pressure. The pilot piston (18) is
appropriately sealed with seals which slide against the inner
surface of the housing (12) and the outer surface of the inner
tubing (11).
[0057] The pilot piston (18) is biased towards its closed position
by a mechanical spring (26), or a gas spring (28), or a combination
of a mechanical spring and a gas spring. As shown in FIG. 2, a
pilot pressure chamber (28) is filled with a gas, preferably an
inert gas such as nitrogen, through a valve (24), and resists
upward movement of the pilot piston (18). The external pressure in
the casing annulus required to activate the pilot section (13) must
overcome the closing pressure, which is the sum of the gas pressure
in chamber (28) and the pressure exerted by the mechanical
spring.
[0058] To activate the crossover valve assembly, gas (G) is
injected into the casing annulus until the annular pressure is
greater than the closing pressure. The injected gas bears on the
pilot piston (18) through the external pressure opening (22), and
the pilot piston (18) is urged upwards as injected gas fills the
pilot chamber (23), until the external pressure equals the closing
pressure exerted by the mechanical spring and the gas spring.
[0059] As the pilot piston (18) unseats, the injected gas in the
pilot chamber (23) then travels through the pup joint fluid passage
(17) and enters an activation chamber in the power section (14),
bearing upon the power piston (30), which is also a sealed
concentric sliding piston. In one embodiment, the power piston is
biased in a closed position by a mechanical spring (31).
[0060] The power piston (30) pushes against a mandrel (32) having a
valve face (34) which is seated against an injection gas inlet (36)
through the outer housing. The injection gas inlet may be provided
in a circumferential groove (38) around the outer housing which has
an angled conical section. The valve face (34) has a matching
conical section which sealingly engages the injection gas inlet
(36) when closed.
[0061] As injected gas (G) in the casing annular space enters the
power section (14) through gas inlet (36), it proceeds through the
valve assembly between the power section inner tubular (11A) and
the outer housing (12) until it reaches the redundant check valve
or RC valve (50). The injected gas has sufficient pressure to
unseat the , and pass through crossover port (52) and enters the
internal production flow path of the valve (10). The RC valve (50)
is biased closed by a mechanical spring (51), the force of which
may be overcome by the injected gas pressure. The RC valve (50) is
shown seated (closed) in FIG. 6 and unseated (open) in FIG. 8.
[0062] When the external annular pressure outside the valve
assembly drops below the closing pressure of the pilot section, the
pilot piston (18) will be urged towards its closed position until
it seats against the valve seat (20), which initiates the crossover
valve closure sequence. If the annular pressure continues to drop,
the fluid in the pup joint fluid passage (17) and the activation
chamber is allowed to slowly equalize to the lower external annular
pressure through a restrictive bypass (42) which exists between the
power section inner tubular (11A) and the outer housing (12) around
the power piston (30). Once the pressure in the activation chamber
is lower that the biasing force exerted by the power section
mechanical spring (31), the power piston (30) returns to its closed
position. When the power piston returns to its closed position, the
valve face (34) seats on and closes the injection gas inlet (36).
The RCV valve (50) will then close and the crossover valve assembly
(10) again isolates the annulus from the production tubing.
[0063] The restrictive bypass (42) is always open, but provides
sufficient resistance to gas flow to allow gas pressure from the
pilot section to open the power piston through the activation
passage, while allowing equalization within a reasonably short
period of time, in one embodiment, in the order of a few
minutes.
[0064] Therefore, the valve assembly (10) will open an injection
opening at annular pressures above the pilot section closing
pressure, and will begin a closing sequence when the annular
pressure drops below the closing pressure. In one embodiment, the
closing pressure of the pilot section of the valve is adjusted by
adjusting the strength of the mechanical spring and the gas spring,
if both are used. The selected closing pressure may be determined
by considering the well depth, annulus volume available and
gas/liquid ratios. In one embodiment, the closing pressure of the
pilot section will be set significantly higher than the minimum
tubing pressure], thereby ensuring no sour gas in the production
tubing can escape into the annulus through the valve assembly (10).
For example, the closing pressure may be set at 500 kPa over the
minimum tubing pressure. This will ensure the valve assembly is
always closed, except when there is significant higher pressure in
the annulus, which is particularly important in the absence of the
inhibited annulus fluid to prevent sour gas migration into the
annulus. In addition, the valve may be equipped with isolation
mechanisms (or barriers) between the production tubing inside
diameter where sour gas resides and the annulus which is required
to remain sweet.
[0065] In one embodiment, the gas spring can be charged to a very
high pressure during assembly of the valve assembly (10), before
use in the field, and can then be adjusted to a desired pressure
for the particular downhole conditions it will encounter before
installation down hole. The mechanical spring provides a fixed
closing pressure, while the gas spring may provide a variable
customizable closing pressure.
[0066] In one embodiment, the gas spring may be connected with gas
capillary lines, a regulator, and a controller. The gas spring may
thus be charged with gas to increase the pilot closing pressure, or
gas may be discharged to decrease the pilot closing pressure, after
installation, as desired.
[0067] Therefore, in one embodiment, the crossover valve comprises
three actuating components, the pilot section, the power section
and the RC valve, which interact by gas pressure and not physical
linkage. External pressure causes the pilot section to expose an
activation chamber to the external pressure, thereby activating the
power section, which opens an injection opening which then opens
the RC valve.
[0068] In one embodiment of operation, and with reference to FIG.
1, a bottom hole check valve (8A) is placed into the bottom of
production tubing string, which functions to prevent gas injected
from surface entry into the formation when the well is completed,
but does allow gas flow from the formation into the tubing
string.
[0069] The crossover valve (10) assembly can be run using wire line
techniques or coiled or jointed tubing techniques that are well
known in the industry and need not be further described here. If an
existing sliding sleeve is part of the production string, it may be
opened. Alternatively, the tubing (2) may be perforated above the
isolation packer (3). The valve (10) is landed above the isolation
packer (3), level with an open sliding sleeve or with tubing
perforations. The valve is located in between two thru-tubing
pack-offs (4, 5) which isolate the production tubing (2) above and
below the valve (10). Any gas from the annulus can only enter the
production tubing through the valve (10). Suitable anchor and
packer configurations are described, for example, in co-owned U.S.
Pat. No. 7,347,273 B2, the entire contents of which are
incorporated herein by reference (where permitted).
[0070] Any inhibited fluid in the annulus may be removed using
conventional means, such as by circulation of nitrogen gas.
[0071] Once the downhole equipment has been installed and any
inhibited fluid has been removed, a sweet gas compressor (102) can
compress low volume gas from the instrument supply line (104) and
inject it down the casing tubing annulus. Once the annular pressure
exceeds the closing pressure of the crossover valve (10), the
injected sweet gas (G) will pass through the valve (10) into the
production tubing, overcome the flowing bottom hole pressure, and
cause the bottom check valve (8A) to close. Thus, all the sweet
annular gas (G) will move upwards in the production tubing. This
will increase the gas velocity, preferably to above the critical
rate, and drive any liquid column in the production tubing to the
surface.
[0072] Once the liquid column is produced, the pressure in the
annulus may be reduced, closing the valve (10), while still
maintaining a positive pressure differential against the production
tubing. With the liquid hydrostatic column removed from the well
bore, the well can now produce to full potential through the bottom
check valve (8A). The production cycle is repeated when the
injected gas pressure in the annulus has reached the required
pressure to open the crossover valve (10) again.
[0073] A plunger assembly (not shown) may be introduced into the
tubing string to allow the well to be operated at lower gas
velocities, as is well known in the art. The plunger acts as an
interface between the liquid column and the injected gas. Because
the plunger is a dynamic seal with close tolerance between the
plunger body and the tubing wall (as opposed to perfect seal), it
still requires velocity to move the liquid up hole, however the
cross sectional area of the plunger coupled with the gas velocity
trying to pass the outside creates a differential pressure from
below which drives the plunger and the liquid column to
surface.
[0074] In an alternative embodiment, a crossover valve assembly
(100) includes the components described above, and further
comprises an electrical control module (110) or ECM, The ECM (110)
is operative to modify operation of the crossover valve (100),
either by controlling delivery of pilot gas to charge or discharge
the pilot gas spring, or by otherwise modulating or overriding
operation of the pilot section, or both.
[0075] As shown schematically in FIG. 9, a pilot gas regulator
(120) is connected by a capillary line (122) to a supply of pilot
gas, which may be at the surface. A pilot controller (not shown)
connects to the regulator (120) by a control line (124), and
actuates the regulator (120) to open or close a valve (126) to
charge or discharge the gas spring as required.
[0076] Another control line (130) connects a controller (not shown)
to a solenoid (132), which actuates a pilot control valve (134).
When open, the pilot control valve (134) exposes the pilot section
of the crossover valve assembly (100) to injection gas pressure
(102) in the casing annulus. If closed, the pilot section remains
isolated from the casing annulus pressure, and therefore, the pilot
section cannot actuate the power section to open the crossover
valve. Thus, the controller can deactivate a crossover valve
assembly (100) while still injecting as into the casing annulus
above the closing pressure of the pilot section,
[0077] In an alternative embodiment, as shown schematically in FIG.
10, the pilot section (202) of the crossover valve assembly (200)
is directly regulated by a control signal received over a control
line (204) which connects to a controller (not shown). A pressure
transducer (208) senses injection gas pressure (206) in the casing
annulus and may connect to the control line (204) via a controller
(209) and a relay (210). Accordingly, at a pre-determined pressure
in the casing annulus, as sensed by the pressure transducer, the
controller will actuate the solenoid (212) to release the pilot
section. The injected gas will then activate the pilot section as
described above. In this case, the pilot section closing pressure
is determined by the combined action of the pressure transducer,
controller and solenoid, and not by any physical biasing means
contained in the pilot section. A control signal may then close the
pilot section after a desired length of time, or at a
pre-determined pressure as determined by the pressure
transducer.
[0078] In one embodiment, the system may comprise electronic
monitoring and pressure recording to determine when the system
operates, such as, for example, by using a PLC (Programmable Logic
Controller) with various analog and digital inputs and outputs,
which can read and record signals from external sensors such as
pressure transducers or flow meters. These transducers constantly
sample the well pressures and will signal the PLC control box to
open casing valves to flow or shut in. The PLC may also have a
proximity switch which detects the plunger arrival at surface and
records times and flow rates. With these electronic instruments and
control, the well can be left with no human intervention once the
flow cycles are set into the controller. These set pressures and
times can be adjusted to suit the changing well conditions.
[0079] Alternate means exist of completing this production workflow
including, but not limited to a locking and sealing mandrel
assembly (as is well known in the art) to engage and seal in an
existing selective profile nipple integral to the production tubing
string. This would replace the tubing packer (5) depicted in FIG.
1. This completion is possible if a selective profile nipple exists
and is easily accessible in the wellbore relative to the location
of the communication ports through the production tubing wall. In
another alternative, the tool string may be landed across an open
sliding sleeve providing communication through the wall of the
tubing from the annulus. All of the elements of the tool string may
be designed to pass through the largest standard selective profile
nipple size in order to easily facilitate landing said tool string
across an existing sliding sleeve (equipped with profile nipple) or
below an existing profile nipple in the event that complex wellbore
geometry is encountered.
* * * * *